Heat exchanger

ABSTRACT

The heat exchanger (100) encompasses an vertical housing (1), in which a bundle (50) of parallel pipes (30) is provided, which pipes extend between a lower pipe header (10) and an upper pipe header (20) and can be flowed through by a hot process gas that enters at the intake (4) and exits at the outlet (9). At the outer circumference of the pipes (30), the heat of the process gas is transferred to a fluid cooling medium, for example air, that enters the housing (1) at the intake (17) and exits it at the outlet (24). The highest pipe (30) temperatures occur in the region of the lower pipe header, which, for this reason, is configured as a double pipe header (10) that is cooled by boiling water (FIG. 1).

The invention relates to a heat exchanger of the type for coolingprocess gases containing finely-dispersed solid components at hightemperatures, preferably between 800° and 1200° C., particularly forcarbon black production.

BACKGROUND OF THE INVENTION

Heat exchangers of this type are known from, for example, GermanPublished, Non-Examined Patent Application DE-OS 27 25 045, GermanPatent DE-PS 29 48 201 and U.S. Pat. No. 3,364,983. These heatexchangers, which are used in systems for carbon black production, arethe point of departure for the invention. The bulk of the carbon blackserves as a filler in the tire industry. It is obtained by means ofsubstoichiometric combustion of a heavy oil residue (feed stock). Theprocess gas that forms during combustion carries along the carbon black,in finely-dispersed form, and is conveyed through the pipes of the heatexchanger. The temperature of the process gas as it enters the heatexchanger is in a range of approximately 800° C. to 1200° C., typicallyin a range of 800° to 1050° C. As it passes through the pipes, theprocess gas is cooled to temperatures in an order of magnitude of 550°to 650° C. as heat exchange occurs. The exchange medium, generallycooling air (process air), flows along the outer circumference of thepipes, in the opposite direction of the process gas, and is warmedduring the process from, for example, between 40° and 60° C. to between700° and 800° C. Air heated in this way can be used as preheatedcombustion air.

Some types of carbon black carried along by the process gas have thetendency to deposit on and clog the surrounding surfaces. This isparticularly the case for the flow supply pipes; consequently, they areequipped with a cleaning apparatus, by means of which a blast of steamor other compressed gas can be sent through the pipes at regularintervals to loosen the deposited carbon black from the wall and entrainit. Cleaning apparatuses of this type are known from the three citedpublications.

In practice, the pipes, and thus the entire heat exchanger, have aconsiderable length of approximately 8 to 12 meters, and are combined toform a pipe bundle of approximately 50 to 100 in a boiler-type housing,which is generally cylindrical. The assemblies can be arrangedvertically or horizontally.

While carbon black production was the starting point for the invention,similar problems can also occur in other chemical and combustionprocesses in which process gases are formed that containfinely-dispersed solid components and are to be cooled.

A critical feature of heat exchangers of this type are the pipe headersarranged on the side of the process gas intake chamber, which are in ahigh temperature range and must endure a temperature difference ofseveral 100° C. on their two sides. In addition, the geometrical shapeof the pipe headers as a plate provided with multiple perforations isunsuitable for continuous thermal exposure. In the past, therefore,cracks appeared repeatedly in the pipe headers. This led to theformation of air on the one hand and carbon-containing gas on the otherhand, as well as the presence of high temperatures and excessivecombustion inside the heat exchanger, resulting in a breakdown of thesame within a short time. When this occurs, of course, the entireupstream and downstream production line must be halted. The resultingdamage extends well beyond merely replacing the heat exchanger, whichalready represents a large unit associated with a correspondinginvestment.

From DE-OS 22 23 805, it is already known to reduce the temperaturestress of the pipe header disposed on the side of the process gas intakechamber by configuring the pipe header as a double pipe header flowedthrough by a cooling medium. No details are disclosed regarding thecooling medium and its conduction. If the cooling medium is flowingwater, the cooling performance is limited in the region of the doubleheader, because the cooling performance is a function of the limitedtransfer of heat from the steel of the pipes and the headers to theliquid water.

SUMMARY OF THE INVENTION

It is the object of the invention to improve the operating reliabilityof a generic heat exchanger by improving the cooling in the region ofthe double pipe header.

This object is accomplished by the heat exchanger for cooling processgases of the present invention.

With boiling-water cooling, it is possible to repeatedly cast water or awater/steam mixture against the upper pipe header of the double pipeheader, where it evaporates and, in the region of the critical weldedpoints of the pipes, carries off essential quantities of heat by wayevaporation. The temperature of the double pipe header arranged on theside of the process gas intake is thereby decreased considerably,causing the material to attain a range of better mechanical properties.The boiling-water cooling is effected by the partial filling of thedouble pipe header with water.

The two individual pipe headers of the double pipe header are arrangedvertically one above the other, and the cooling water fills the spacebetween the pipe headers, or above the lower pipe header, to a specificlevel. The lower ends of the pipes extend vertically through the doubleheader. To permit control of the pressure in the double header, thesteam is condensed externally by means of air or water. The heatobtained in this manner can be used further in some other way. Thecondensate is circulated back into the double header, so the quantity ofcooling water of the double header circulates of its own accord,eliminating the need for pumps.

The control of the cooling performance can be effected in a mannerwherein the condenser is water cooled and a thermal element thatmeasures the temperature of the water in the double pipe header isprovided for controlling the quantity of cooling water supplied to thecondenser.

Because thermal stress on the pipes is the greatest in the vicinity ofthe gas entrance, it is advisable to provide in the area of the doublepipe headers loosely-inserted, inner protective coverings, which can beeasily exchanged, and prevent the process gas from directly acting uponthe inner pipe circumference on the first segment of the path of flow,where the highest temperatures occur.

To avoid having to perform complicated disassembly on the double pipeheader during an exchange, specifically involving cutting work, it isadvantageous for the pipes to be surrounded by separating pipesconnected tightly to the two pipe headers of the double pipe header.

The double pipe header, along with the separating pipes penetrating it,constitutes a closed unit in which the long heat exchanger pipes can beeasily exchanged.

The separating pipes, however, have the additional task of slowing thetransfer of heat from the starting region of pipes into the coolingwater in the double pipe header.

In the double pipe header, the cooling water can enter the space betweenthe socket and the separating pipe through the opening at the lower edgeof the socket and be evaporated by the contact with the lower part ofthe hot separating pipe, whereupon the created steam shoots upward inthe narrow space between the socket and the separating pipe, and theentrained water/steam mixture assures an effective thermal dissipationfrom the outer circumference of the separating pipe, and cools thethermally high-stressed welded point of the separating pipe in the upperpipe header of the double pipe header.

The invention discloses the manner in which the cooling medium, in mostinstances cooling air, can be made considerably effective if it isconducted through the annular space between the pipe and the jacket, andhow the cooling medium can be brought into and back out of thisintermediate space.

The jacket is an additional pipe that normally surrounds the respectiveheat exchanger pipe concentrically with spacing, leaving a sufficientflow cross section for the cooling medium between the two pipes. Theinner diameter of the jacket can be, for example, 1.2 to 1.5 times theouter diameter of the respective pipe. The additional heat transfersurface at the inner circumference intensifies the transfer of heat fromthe pipes to the cooling medium as compared to the case in which thepipes are in contact with the cooling medium flow without a jacket. Thejacket heats itself, and for its part radiates and, moreover, reflectsthermal radiation emitted from the outer circumference of the pipes. Ithas been determined that the mere presence of the tubular jacketsclearly permits an increase in the thermal transfer performance.

In principle, the space between the pipes and the jackets can be flowedthrough by the same flow as in the pipes or by counterflow. To avoidexcessive temperature differences in the region of the double pipeheader, which is stressed by high temperatures anyway, the counterflowis generally recommended.

A favorable way to introduce the flow of the cooling medium into theintermediate space is also disclosed as is an important embodiment ofthe jacket arrangement.

With the additional heat transfer surfaces in the intermediate space,the heat transfer performance can be increased up to 20% with respect topipes not provided with a jacket, which means that the pipes and theentire heat exchanger can be configured up to 20% shorter, assuming thesame heat transfer performance. This is a strong argument from aneconomic argument, considering the great length of the heat exchanger of8 to 12 m.

The cold and warm states of the pipes are separated by about 1000° C.Because of the length of the pipes connected to the double pipe header,displacements result at the upper pipe end due to differences in thermalexpansion of the pipes and the surrounding housing in an order ofmagnitude of 40 mm. Compensators are useful for combating this, forexample the known metal beam compensators.

A further important embodiment of the heat exchanger of the invention isa steam-cleaning apparatus which is known per se in heat exchangers, ascan be seen in the three publications cited at the outset.

Alternative options of arranging the steam cleaning apparatus are alsodisclosed including placing the apparatus at the end of each pipe thatprojects into the process gas outlet chamber or terminating into theprocess gas intake chamber.

Another embodiment includes the steam nozzle that is concentric to thepipe axis, is aimed into the pipe and does little to impede the flow ofprocess gases into the pipe. The nozzles arrange before the terminationof each pipe in the process gas intake chamber, the steam line of whichnozzle is guided through the process gas intake chamber in the segmentadjacent to the steam nozzle. This embodiment is preferred because ofsimplicity and problem-free integration into a double pipe header thathas been cooled by boiling water.

Leading the steam line through the process gas intake chamber, in whichthe high temperatures of the entering process gas dominate, placesconsiderable stress on the pipes of the steam line.

For this reason, it is advisable to utilize the configuration wherein inthe double pipe header the steam line is guided close to the relevantpipe, guided downward therethrough the pipe header adjacent to theprocess intake chamber and into the process gas intake chamber, is bentback theretoward the pipe header and supports the steam nozzle at a freeend. Further, in the process gas intake chamber, the steam line can forma 180° pipe bend whose legs are parallel to the pipe axis. This has theadvantage that only the last, short segment of the steam line needextend in front of the steam nozzle in the process gas intake chamber.

A jacket pipe which surrounds the steam line with radial spacing is alsoa contemplated arrangement; it creates an intermediate space, which isfilled with the hot water standing in the double pipe header. In thelast part of the jacket pipe extending in the process gas intakechamber, this water evaporates immediately, and, in the form of steam ora water/steam mixture, shoots through the ascending pipe and into thesteam chamber, because the flow resistance for the water or water/steammixture is less on this side with correspondingly adapted crosssections. In this way, the pipe bend and the nozzle region areconstantly flowed through by hot water, steam or a water/steam mixtureand cooled. No pumps are required to transport this cooling medium.

To prevent an erosive attack of the part of the pipe bend of the jacketpipe that extends through the process gas intake chamber, as well as ofthe nozzle, it is advisable to surround this region with an appropriateinsulation.

To prevent the double pipe header from emptying when damage occurs tothe ascending pipe or the part of the jacket pipe extending in theprocess gas intake chamber, the end of the jacket pipe on the side ofthe double pipe header can be used as an overflow.

A cross section relationship is recommended for achieving the desiredflow-through of the space between the jacket pipe and the steam line andthe adjoining ascending pipe.

The side of the pipe header of the double pipe header facing the processgas intake chamber, which faces the hot process gas that is flowing in,is thermally high-stressed, and expediently has a fireproof sheathingwhich, in a practical embodiment, can be configured as uniformly shaped,fireproof molded bodies, for example hexagonal stones having a centralopening for access to the respective heat exchanger pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated in the drawing figure.

FIG. 1 shows a vertical section through an upright heat exchanger;

FIG. 2 shows a detailed view from the upper region of FIG. 1;

FIG. 3 shows a detailed view from the lower region of FIG. 1;

FIG. 4 shows an enlarged view from the region of the double header, withthe associated steam guide;

FIG. 5 shows a further enlarged view from the region of the double pipeheader;

FIG. 6 shows a section according to line VI--VI in FIG. 5;

FIG. 7 shows a view from below of a fireproof molded body according toFIG. 5; and

FIG. 8 shows an enlarged view of a modified embodiment of the heatexchanger corresponding to FIG. 5.

PREFERRED EMBODIMENTS

The heat exchanger indicated in its entirety by 100 in FIG. 1encompasses an upright, cylindrical housing 1 of sheet steel andarranged on a substructure 2. A cylindrical process gas intake chamber3, which has approximately the same diameter as the housing 1 and isopen to the top, is arranged inside the housing. The hot process gas,for example having a temperature of 1000° C., enters the substructure 2laterally at the intake 4, in the direction of arrow 5, and is divertedupward in the substructure into the process gas intake chamber 3. Thesubstructure 2 has a fireproof lining 6.

A double pipe header 10 comprising a horizontal, lower pipe header 11and a horizontal pipe header 12 arranged approximately 30 cm above it isconfigured at the lower end of the housing 1, and extends perpendicularto the housing axis A. The lower side 13 of the pipe header 11, whichfaces the process gas intake chamber 3, is provided with a ceramicsheathing 14 that has conical vent openings 15, as explained in detailbelow in conjunction with FIG. 5. Only one opening of this type isindicated in FIG. 1.

An upper pipe header 20 that partitions off a process gas outlet chamber7 from the interior of the housing 1 is provided near the upper end ofthe housing 1. The process gas introduced at the intake 4 collects inthe process gas outlet chamber 7 and leaves it at the outlet 9, in thedirection of arrow 8.

The interior of the housing is filled by a pipe bundle 50. The pipebundle 50 encompasses closely-bundled pipes 30 distributed over thecross section of the housing 1 and extending parallel to the axis A; ofthese pipes, only one is shown in FIG. 1, and a few others are indicatedby their center lines. Depending on the design of the heat exchanger100, the pipe bundle 50 will comprise, for example, 50 to 100 bundledpipes 30.

The pipes 30 are welded at their lower ends in the lower pipe header 11,and terminate open in a respectively associated, conical vent opening 15of the fireproof sheathing.

The pipes 30 extend over the entire height of the housing 1, andterminate open in the process gas outlet chamber 7, above the pipeheader 20. The process gases introduced at the intake 4 enter the pipes30 at the lower end and exit the pipes 30 at the upper end to enter theprocess gas outlet chamber 7. Because the pipes 30 become very hot dueto the high temperature of the process gases, and have a considerablelength of, for example, 9 meters, considerable thermal expansions occur,since the housing 1 does not possess the high temperatures.Displacements in an order of magnitude of 30 to 50 mm must be taken intoaccount at the ends of the pipes 30 projecting into the process gasoutlet chamber 7. The vent opening at the upper pipe header must becompletely sealed in order to prevent the mixing of the process gasesand the cooling air and thus combustion. For this reason, compensators31 on the underside of the upper pipe header 20 are provided with metalexpansion bellows.

In the upper region of the housing 1, a cooling air intake chamber 16 isformed by an intermediate pipe header 21 arranged at a distance ofapproximately 10 centimeters beneath the upper pipe header 20. Theintake chamber can be supplied with cooling air via a lateral intake 17,in the direction of arrow 18; this air has a normal or only slightlyincreased temperature.

Each pipe 30 is surrounded by a jacket 40 in the shape of a further pipewhose inner circumference leaves spacing around the outer circumferenceof the pipe 30. The jackets 40 extend over nearly the entire height ofthe housing 1, and end immediately above a fireproof lining 19 on thetop side of the upper pipe header 12 constituting a part of the doublepipe header 10.

A cooling air outlet chamber indicated in its entirety by 23 ispartitioned by an intermediate pipe header 22 arranged with spacingabove the pipe header 12; the height of this chamber essentiallycorresponds to that of the cooling air intake chamber 16, which thecooling air enters from the lower, open ends of the jackets 40 and fromwhich it can be carried off at an outlet 24 in the direction of arrow25. The jackets are secured to the intermediate pipe header 21 and hangfreely downward from it. The distance of the lower end 40' from thefireproof layer 19 takes into account the thermal expansion that occurs.Sufficient space for the exit of cooling air must be provided at alltimes. At the upper end, the jackets 40 are expanded in a funnel shapeby means of beading, as shown at 41 in FIG. 2, in order to facilitatethe entrance of the cooling air into the intermediate space between thepipe 30 and the jacket 40.

Because the pipes 30 and the jackets 40 possess a considerable height,an additional intermediate pipe header 26 or a plurality thereof isprovided and distributed over the height in order to stabilize the pipebundle 50.

The flue gas outlet chamber 7 is closed to the top by a flanged lid 34which, in one embodiment, simultaneously serves as a carrier forsteam-cleaning apparatuses 33, by means of which a blast of steam can besent into the pipes 30 from above at intervals of, for example, oneminute in order to loosen deposits of finely-dispersed, solid materials,such as carbon black, that are starting to build up on the inner wall,and force them out downward through the pipe 30.

FIG. 4 shows the double pipe headers 10 in somewhat greater detail, aswell as the control of the boiling-water cooling omitted in FIG. 1. Thespace between the pipe headers 11 and 12 is filled with water 28 to afill level 27. The pipes 30 are surrounded over the height of the doublepipe header 10 by separating pipes 35, which are tightly welded to thepipe headers 11, 12. The pipes 30 are simply penetrated by theseparating pipes 35, and do not come into direct contact with thecooling water 28.

The separating pipes 35 are in turn surrounded, with a small radialspacing, by a socket 36 that is expanded cylindrically at the top andslightly conically at the bottom and serves to bring about theboiling-water cooling of the lower end of the separating pipe 35 or thepipe 30, as ensues in detail from FIG. 5.

The hot flue gases enter the pipes 30 from below, in the direction ofarrows 37, thus heating their lower end intensely. The water 28 beginsto boil. The resulting steam is drawn out of the steam chamber above thewater level 27, via the line 29, and supplied to a water-cooledcondenser, in which it is condensed; the condensate is subsequentlyconducted back into the double pipe header 10 via the line 39.

The temperature in the double pipe header 10 is dependent on theprevailing pressure. It is measured by a thermoelement 42 and convertedinto an electrical signal at a converter 43, by means of which a motor44 can be operated for the purpose of controlled adjustment of a valve45. The valve 45 determines the quantity of cooling water supplied tothe condenser 38 from the H₂ O network in the direction of the arrow,and therefore the cooling performance of the condenser 38 in relation tothe heating performance of the flue gases in the double pipe header 10.The cooling water evaporates or vaporizes in the condenser 38 and eitherescapes into the atmosphere A or is utilized as warming water. The morecooling water is supplied, the greater the condensation output. Thepressure in the double pipe header 10 drops. The delivery of heat by theprocess gases counteracts this. An equilibrium or a desired water andsteam temperature that can be adjusted by corresponding operation of thevalve 45 results in the double pipe header 10. In most cases, a pressureof 15 to 20 bar is maintained in the double pipe header 10,corresponding to temperatures of 180° to 200° C., which are favorablefor preventing corrosion caused by condensing components of the processgases.

It can be seen in FIG. 5 that the separating pipe 35 surrounding therespective pipe 30 is welded tightly into the two pipe headers 11, 12 ofthe double pipe header 10. The upper three-quarters of the height of theseparating pipe 35 has an increased inner diameter, so fireproofinsulating material 46 can be accommodated between the outercircumference of the pipe 30 and the inner circumference 35' of theseparating pipe 35 there; this insulating material is covered toward theinside by a thin-walled pipe 47, so the pipe 30 can be inserted fromabove without problems. At the lower end 30", the pipe 30 is weldedtightly to the inner, lower edge of the separating pipe 35 at 35".Inside the pipe 30, an inner, protective sleeve 48 consisting ofthin-walled pipe material is arranged over the height of the double pipeheader 10. The outer circumference of this sleeve leaves a small spacingfrom the inner circumference of the pipe 30, and has a beaded edge 49above the fireproof sheathing 19, the edge being oriented outwardly forguidance purposes. At the lower end, the protective sleeve 48 is seatedon a shoulder 51 of the fireproof molded bodies 52, which form thefireproof sheathing 14. In the region of the lower end, a fireproofinsulating material 53 is arranged between the outer circumference ofthe protective sleeve 48 and the inner circumference of the pipe 30.

The outer, smooth-cylindrical separating pipe 35 is surrounded by asocket 36 to achieve boiling-water cooling; this socket is cylindricalin approximately the upper half, surrounds the outer circumference ofthe separating pipe 35 with about 2 to 6 mm of play, about 4 mm in theexample. In the lower region, the socket 36 expands slightly conically.It stands on the pipe header 11 and has openings 54 at the lower edgethat permit the entrance of water 28 into the chamber 55 between theouter circumference of the separating pipe 35 and the innercircumference of the socket 36. At the upper edge 36', the socket 36leaves spacing in an order of magnitude of 1 cm from the underside ofthe pipe header 12. The water entering at the openings 54 evaporates atthe hot outside of the separating pipe 35, and the steam or, possibly, asteam/water mixture in the space between the inner circumference of thesocket 36 and the outer circumference of the separating pipe 35 shootsupward, maintains the outer circumference of the separating pipe 35 atessentially the steam or water temperature, and, in particular,purposefully cools the region of the welded point between the upper edgeof the separating pipe 35 and the pipe header 12.

In the exemplary embodiment, the fireproof sheathing 14, which isimpacted by the hot process gases flowing toward it from the process gasintake chamber 3, comprises hexagonal molded bodies 52 having uniformcontours, each of which is associated with a pipe 30. The molded bodies52 cover the underside of the pipe header 11 so as to seal it. They havea conically-narrowing opening 15 that tapers down to the inner diameter56 of the protective sleeve 48. The fireproof molded body hasperforations 57 that are penetrated by pins or hooks welded to theunderside of the pipe header 11. The molded bodies 52 are thereforesuspended beneath the pipe header 11.

It can be seen from FIG. 6 that the inner circumference of the jacket 40leaves a sufficient spacing from the outer circumference of the pipe 30to assure a sufficient flow cross section in the intermediate space 58for the cooling air entering from the cooling air intake chamber 16.Additional heat transfer surfaces 60, 60' are provided in theintermediate space 58. In the upper half of FIG. 6, the heat transfersurfaces 60 are formed by the surface of a piece of sheet metal 59 thatis corrugated in a plane perpendicular to the axis of the pipes 30, 40and is in heat-conducting contact with the outer circumference of thepipe 30. In the example in the lower half of FIG. 6, the heat transfersurfaces 60' are the surfaces of supports 59', webs or ribs distributedover the outer circumference of the pipe 30 and in heat-conductingcontact with it. These elements are flowed around by the cooling medium,and leave free a corresponding flow path between themselves. With theadditional heat transfer surfaces 60, 60', the transfer of heat from theouter circumference of the pipe 30 to the cooling medium, generallycooling air, flowing through the intermediate space 58 can be notablyincreased.

In a concrete exemplary embodiment, the outer diameter of the pipe 30 isapproximately 90 mm and the inner diameter of the pipe 40 isapproximately 115 mm. The pipes 30, 40, the sheet metal pieces andsupports 59, 59' and the components of the double pipe header 10comprise suitable, temperature-resistant steels.

Each pipe 30 is allocated a steam-cleaning apparatus that is disposed atone pipe end and delivers a blast of steam into the pipe from time totime to eliminate deposits forming at the inner pipe circumference.

In an exemplary embodiment indicated on the left side of the housing 1in FIG. 1, is a steam-cleaning apparatus 33, arranged above the upperend 30' of a pipe 30, as mentioned above. The steam-cleaning apparatus33 encompasses a cylindrical housing 70 that is welded into the lid 34,coaxially to the axis of the associated pipe 30. A sealing plate 80formed by a perforated disk is arranged at the lower end; when steampressure is present, the plate is displaced forward toward the intake78, is seated at the upper end 30' of the pipe 30 and can serve todirect a blast of steam down into the interior of the pipe 30.

An alternative embodiment of a steam-cleaning apparatus 63 that deliversa blast from below is indicated in FIG. 1, in the region of the doublepipe header 10, and shown in a more detailed representation in FIG. 8.The reference numerals are identical for parts corresponding to those inFIG. 5.

The steam line 61 is guided through the steam chamber 27' left openabove the water level 27 until it is in the vicinity of the respectivepipe 30, and bends there into a downward-pointing leg 62 that leadsdownward through the pipe header 11 and the fireproof sheathing 14 andinto the process gas intake chamber 3, in which a 180° pipe bend 64adjoins the line. A steam nozzle 65 is attached, concentrically to thepipe 30, at the free, upward-pointing leg 62' of this pipe bend.

In the region adjacent to the steam nozzle 65, the steam line 61 issurrounded concentrically by a jacket pipe 66, which likewise leads outof the double pipe header 10 into the process gas intake chamber 3 andforms a 180° pipe bend 67 there. The jacket pipe 66 leaves a space 68from the outer circumference of the steam line 61. The end 66' of thejacket pipe 66 surrounding the leg 62 is located with spacing above thepipe header 11 and with spacing beneath the water lever 27. Therefore,water 28 can enter the intermediate space 68 at the upper end 66', inthe direction of the arrows, and fill the space. The position of theupper end 66' with spacing above the pipe header 11 provides for anoverflow function that prevents the double pipe header 10 from emptyingcompletely if a line break occurs in the region of the process gasintake chamber 3.

The steam nozzle 65 is likewise surrounded by a jacket 69, whoseinterior 71 is connected to the intermediate space 68 and which has alateral connection 72 adjoined by an ascending pipe 73 that bends upwardand enters the double pipe header 10 closely next to the pipe 30 orsocket 36. The upper end 73' of the ascending pipe 73, which terminatesopen, is arranged above the water level 27 and just beneath the upperpipe header 12.

The segment of the jacket pipe 66 extending in the region of hightemperatures in the process gas intake chamber 3 can be surrounded by aninsulation 74. This also applies, of course, to the correspondingsegment of the ascending pipe 73.

From time to time, a blast of steam is introduced into the steam line61, in the direction of the arrow. This steam enters the pipe 30 frombelow and loosens deposits sticking to the inner circumference.

Water from the double pipe header 10 enters the intermediate space 68 atthe upper end 66' of the jacket pipe 66, in the direction of the arrow,and is immediately vaporized in the region of the process gas intakechamber 3. Because the flow resistance for the steam is less in theregion of the ascending pipe 73 than in the region of the intermediatespace 68, the formed steam enters the steam chamber 27' in the directionof the arrow 75 and exits toward the upper pipe header 12, not throughthe intermediate space 68 and into the water 28. A result of this is atransport effect, the consequence of which is that new cooling hot water28 is always transported through the intermediate space 68 and in thesteam chamber 27' in steam form, so the pipe arrangement 62, 64; 66, 67is maintained at a tolerable temperature. To support this effect, itshould be provided that the cross section of the ascending pipe 73 islarger than the cross section of the annular intermediate space 68.

So that the influx of the process gases into the pipe 30, in thedirection of the arrows 75, is impeded as little as possible, the steamnozzle 65 is arranged with spacing from the lower end of the pipe 30 orthe lower end of the protective sleeve 48 or sheathing 14, and also hasan outer cross-section smaller than the inner cross-section of theprotective sleeve 48.

Having thus described the invention it is claimed:
 1. A heat exchanger for cooling process gases having finely-dispersed solid particles at high temperatures between 800° and 1200° for producing carbon black said heat exchanger including a housing, a bundle of pipes within said housing having opposite ends and extending parallel to one another and closely together for carrying the process gases through the housing, at least first and second pipe headers arranged near the ends of the pipes, transverse thereto and filling the cross section of the housing, the pipes passing axially through said headers in a sealing manner and terminating in open ends, a process gas intake chamber configured at a first end of the housing axially outside of the first pipe header, a process gas outlet chamber configured at a second end of the housing axially outside the second pipe header an intake for a fluid cooling medium that is disposed near the second pipe header, and an outlet for the fluid cooling medium near the first pipe header, wherein the first pipe header is in the form of a double walled pipe header having a first pipe header wall portion and a second pipe header wall portion through which the ends of the pipes pass and in which a cooling medium is present, the improvement comprising a boiling water cooling action being produced in the double walled pipe header, said double walled pipe header being arranged horizontally and partially filled with water creating a steam chamber above said water, said steam chamber being connected to an external condenser with the condensate being fed back into the double walled pipe header.
 2. A heat exchanger as defined in claim 1, wherein said condenser is water-cooled and a thermoelement that measures the temperature of the water in the double walled pipe header is provided for controlling the quantity of cooling water supplied to the condenser.
 3. A heat exchanger as defined in claim 1, wherein said pipes have a loosely-inserted, inner protective sleeve in the region of the double walled pipe header.
 4. A heat exchanger as defined in claim 1, wherein each said pipe in the region of the double walled pipe header is surrounded by a separating pipe over at least a portion of the pipe with a space therebetween, the separating pipe being tightly connected to the first and second pipe header wall portions of the double walled pipe header.
 5. A heat exchanger as defined in claim 4, including fire resistant insulating material in the space between the inner circumference of the separating pipe and the outer circumference of the pipe.
 6. A heat exchanger as defined in claim 1, wherein said separating pipes are vertical and are concentrically surrounded in the region of the double walled pipe header by a socket which at an upper region is radially spaced from the outer circumference of the separating pipe creating an intermediate space, and has an opening to the intermediate space at a lower end of the socket, and has an opening from the intermediate space into the steam chamber of the double walled pipe header at an upper edge of the socket.
 7. A heat exchanger as defined in claim 1, wherein an intermediate pipe header is located beneath the second pipe header to create a first chamber having said intake for a fluid cooling medium, and another intermediate pipe header being located above the first pipe header to create a second chamber having said outlet for the fluid cooling medium, each pipe being surrounded by a tubular jacket in the region between the first and second pipe headers, the jackets open at one end in the first chamber, with spacing from the pipe header, and at the other end in the second chamber, with spacing from the pipe header, so that access exists to a space between the pipes and the respective jackets and the fluid cooling medium can be conducted from the first chamber to the second chamber through the space between the pipe and the respective jacket.
 8. A heat exchanger as defined in claim 7, wherein the first chamber forms a cooling medium intake chamber and the second chamber forms a cooling medium outlet chamber.
 9. A heat exchanger as defined in claim 8, wherein the jackets are beaded in a funnel-like shape at the ends within the cooling medium intake chamber.
 10. A heat exchanger as defined in claim 10, including additional heat transfer surfaces being provided in the space between the pipes and the respective jackets, said surfaces being in heat-conductive contact with the outer circumference of the pipe.
 11. A heat exchanger as defined in claim 10, wherein the additional heat transfer surfaces are a tubular sheet metal formation that is corrugated in a plane perpendicular to the pipe axis.
 12. A heat exchanger as defined in claim 10, wherein the additional heat transfer surfaces are formed by webs that are distributed over the outer circumference of the pipe, are in thermally-conductive connection with the pipe, and leave open a flow path for the cooling medium through the intermediate space.
 13. A heat exchanger as defined in claim 1, wherein the pipes are fixedly and tightly connected to the double walled pipe header, and a compensator is provided on at least the second pipe header in order to receive the thermal expansion of each pipe.
 14. A heat exchanger as defined in claim 1, wherein associated with each said pipe is a steam-cleaning apparatus at one end that delivers a blast of steam into the pipe at selected intervals for the purpose of cleaning deposited material from the inside of the pipe.
 15. A heat exchanger as defined in claim 14, wherein the steam-cleaning apparatus is arranged at the end of each pipe that projects into the process gas outlet chamber.
 16. A heat exchanger as defined in claim 14, wherein the steam-cleaning apparatus is arranged at the end of each pipe terminating into the process gas intake chamber.
 17. A heat exchanger as defined in claim 16, wherein a steam nozzle that is concentric to the pipe axis, is aimed into the pipe and does little to impede the flow of process gases into the pipe is arranged before the termination of each pipe in the process gas intake chamber, a steam line of which nozzle is guided through the process gas intake chamber in a segment adjacent to the steam nozzle.
 18. A heat exchanger as defined in claim 17, wherein in the double walled pipe header, the steam line is guided close to the pipe, guided downward therethrough the first pipe header and into the process gas intake chamber, is bent back toward the first pipe header and supports the steam nozzle at a free end.
 19. A heat exchanger as defined in claim 18, wherein in the process gas intake chamber, the steam line forms a 180° pipe bend whose legs are parallel to the pipe axis.
 20. A heat exchanger as defined in claim 17, wherein in the segment adjacent to the steam nozzle, the steam nozzle and the steam line are surrounded concentrically by a jacket pipe, with radial spacing therebetween, that terminates inside the double walled pipe header beneath the water level so that water can enter the space between the steam line and the jacket pipe, the space between the steam line and the jacket pipe at the steam nozzle is closed apart from an outlet, an ascending pipe being connected at the outlet and is guided back through the first pipe header wall portion into the double walled pipe header and ends open above the water level, with slight spacing from the second pipe header wall portion, and that in the region of the process gas intake chamber, the flow resistance for steam forming in the intermediate space, is less through the ascending pipe than through the intermediate space.
 21. A heat exchanger as defined in claim 20, wherein the radial spacing around the jacket pipe is supplied with an insulation in the region of the process gas intake chamber.
 22. A heat exchanger as defined in claim 20, wherein the jacket pipe projects beyond the first pipe header wall portion in order to create an overflow for the water located in the double walled pipe header.
 23. A heat exchanger as defined in claim 20, wherein a cross-section of the ascending pipe is larger than a cross-section of the space between the steam line and the jacket pipe.
 24. A heat exchanger as defined in claim 1, wherein the underside of the first pipe header wall portion has a fire resistant sheathing.
 25. A heat exchanger as defined in claim 24, wherein the sheathing comprises a plurality of fire resistant molded bodies that cover the underside of the pipe header. 